An industrial turbomachine, such as a gas turbine for generating electricity, generally comprises a plurality of bladed rotor disks and one or more spacer elements, which are aligned along an axis and frontally coupled. The disks and spacer elements are sandwiched by at least one tie rod or bolt. The disks are provided with respective arrays of blades and each defines a compressor or turbine rotor stage.
A multistage assembled compressor rotor includes several rotor disks axially joined together at corresponding annular flanges. The flange contact faces are typically ground to a very tight tolerance flatness in an effort to minimize rotor eccentricity and tilt. During the stacking process, it is possible for the flange faces to be held slightly apart by foreign debris, face damage, thermal irregularities, and other anomalies, thereby forming an air gap between at least a portion of adjoining flange faces. Additionally, each rotor is separately manufactured and is subject to eccentricity between its forward and aft mounting flanges, and is also subject to non-perpendicularity or tilt of its flanges relative to the axial centerline axis of the turbomachine. Individual rotors typically vary in configuration for aerodynamic, mechanical, and aeromechanical reasons, which increases the complexity and difficulty in reducing undesirable eccentricity.
Both eccentricity and tilt of the rotor annular flanges are random and preferably limited to relatively small values. However, the assembly of the individual rotors with their corresponding flange eccentricities and tilts is subject to stack-up and the possibility of significantly larger maximum eccentricity and tilt collectively due to the individual eccentricities and tilts. When the rotor assembly is mounted for mechanical runout testing, adjoining flange joints between individual rotors of the assembly may have tilt and eccentricity from the centerline axis which exceeds the specified limit for the rotors due to stack-up. In this case, the rotor assembly must be torn down and reassembled in an attempt to reduce stackup eccentricities and tilt to an acceptable level.
Upon testing of the assembled rotor, either the net eccentricity and tilt or an inter-rotor eccentricity and tilt may nevertheless exceed the specified limit. This would require teardown of the rotor assembly and re-assembly in an attempt to reduce net eccentricity and stage eccentricity to within acceptable limits. Disassembling and reassembling the rotor are extremely costly during initial production and rebuilding, even of the order of several weeks. Accordingly, it is desired to improve the assembly process of multiple rotors for minimizing eccentricity and tilt thereof from a common axial centerline axis.